In-situ high-resolution 3D imaging of cell or tissue samples offers an important capability to biomedical researchers. It is particularly valuable when the observation can be made at a resolution approaching molecular level with samples that have undergone little morphological or functional change from its natural living state (e.g. cryo preserved), and in combination with the ability to image function-specific features with established labeling techniques. We proposed to develop a tabletop transmission x-ray microscope for in-situ 3D imaging of biological specimens with a resolution of 30 nm and was funded in August 2003 to carry out the Phase I of the project. We have successfully completed the tasks proposed. Specifically, we have modified our commercial tabletop transmission microscope for biological imaging in phase contrast mode and acquired 3D images of a critical-point dried 3T3 fibroblast cell with 70 nm resolution. We propose to advance to Phase II of the project to develop an Alpha unit of a commercial transmission x-ray microscope with the ability to image the 3D structure of frozen hydrated cells or tissue culture samples at 30 nm resolution, with the ability to utilize feature-specific labeling and other contrast-enhancement methods. Sample preparation, imaging protocols, and a comprehensive tomographic reconstruction and 3D data analysis software package will also be developed during the construction of the machine. [unreadable] [unreadable] [unreadable]